You can find a query to find recently changed items under the Tasks gadget that is placed next to the page navigation tree in an default installation.
The "Recently Changed Pages" gadget is not a Dashboard gadget, its a Navigation Pane gadget. Open the Navigation Pane (page tree) and click Settings (cogwheel) > Add Gadget.
Got it. Thanks Linus and Arild!
I can't find the built in gadget "Recently Changed Pages" anywhere in EPiServer 7 http://world.episerver.com/Documents/Manuals/EPiServer%20Platform/EPiServer%207/EPiServer%207%20Platform%20User%20Guide%20(print)%20in%20English.pdf it should be there.
Anyone know how to add it?